WASHINGTON -- Joan Adon didn’t say much when manager Dave Martinez told him at the end of Spring Training he had earned a spot in the Nationals’ starting rotation. Not because he wasn’t happy, but because he was extremely happy. 

“Very exciting,” Adon recalled on Opening Day. “Very exciting.” 

Adon, 23, entered camp with one Major League start on his resume. The right-hander made his debut in last season’s finale against a playoff-hungry Red Sox squad, holding them to two runs with nine strikeouts in 5 1/3 innings. That performance left a lasting impression on the Nationals, who continued to be wowed by their No. 8 prospect in Spring Training.

“Adon, for me, is a guy that’s young that we see that has a future here,” Martinez said last week.

Adon took the next step in his big league future on Saturday when he made his 2022 season debut in a start against the Mets in a 5-0 loss at Nationals Park. Martinez was watching for Adon to get ahead of hitters and hone in on his mechanics. With Adon stretched out to 95 pitches in camp, Martinez also hoped he would throw deep enough to give an already-taxed bullpen a break.

“When he’s good, he’s fastball-heavy,” Martinez said. “He throws his fastball, it’s late, it’s explosive. We always say, it kind of gets on hitters fairly quickly and you can see that. So we like that.”

Adon spanned 4 1/3 frames, allowing four hits, four runs and four walks -- a statistic that stood out to both him and Martinez. He struck out three, hit one batter and tossed two wild pitches. On Adon’s final delivery of the evening -- his 86th pitch -- he allowed a grand slam to slugger Pete Alonso off a 91.2 mph four-seam fastball that put the Mets on the board.

"I was just trying to go and locate the pitch outside, repeat the same pitch I threw on the previous one,” Adon said. “I missed a little bit and it ran over the plate."

Adon threw his fastball for 63 percent of his pitches, with an average velocity of 93.5 mph. He also worked in his slider (28 percent) and changeup (9 percent). Martinez noted Adon was alternating fastball-slider. He wants him to have more trust in his changeup, which pitching coach Jim Hickey will focus on with Adon before his next outing.

"It's always been a good pitch for me,” Adon said. “I feel like I'm throwing it well. It's just I'm missing out of the zone with it. It's doing what I want it to do with the movement. I need to locate it and present it better to the hitters so that they're actually swinging at it instead of taking those pitches."

The Nationals continue to incorporate more young talent into their pitching staff this season, with Adon joining 24-year-old Josiah Gray in the rotation. Cade Cavalli, their No. 1 prospect, also is expected to make his Major League debut this season. The 23-year-old Cavalli was with the Nationals until the final days of camp before they decided he would be better suited building up more innings in Triple-A after just one season of pro ball.

“I just think that Joan’s further in his professional career,” general manager Mike Rizzo said on Friday. “He’s a little bit more polished, and his feet were wet in the big leagues last year. I think that had a lot to do with it. The command of his pitches is important to us, and the fact that he’s pitched in the big leagues had a lot to do with it.”

After waiting the entire 2021 season to take the mound for the Nationals, Adon already has his first start of ‘22 checked off in the first series. With an even-keeled approach and a maturity lauded by Martinez, he is ready to continue growing for his next start.

"This is what I do. This is what I love to do,” Adon said. “This is what I love doing, why would I be nervous?"